Double-sided printing imaging apparatuses usually include a frame, and an imaging unit and a paper conveying mechanism mounted in the frame. The paper conveying mechanism usually includes a paper picking member, a paper conveying member, a paper discharge member, and a double-sided printing paper conveying unit. During the operation of the imaging apparatus, the paper in the paper cassette can be picked up by the paper picking member, conveyed by the paper conveying member to pass through a transfer unit and fixing unit to the paper discharge member. In cases of double-sided printing, the paper that arrives at the paper discharge member usually is conveyed in the opposite direction by the double-sided printing paper conveying unit to a transfer unit to form image on the back side of the paper.
The double-side printing paper conveying unit usually has functions of conveying and skew correction for the paper and can be detachably mounted to an imaging apparatus. In general, a mounting opening for mounting the double-side printing paper conveying unit to an imaging apparatus is disposed on a rear cover of the imaging apparatus.
As shown in FIG. 1, the double-side printing paper conveying unit often includes a guiding part 1 configured to guide the paper, a paper conveyor 2 configured to convey the paper, and an aligner 3 configured to align the sides of the paper. The aligner 3 is fixedly mounted on the guiding part 1. The paper conveyor 2 includes a driving roller and a driven roller. The driving roller is usually rotatably mounted on the guiding part 1 while the driven roller is mounted on a support 4, and the support 4 is fixedly connected to the guiding part 1. The driven roller is usually mounted on the support 4 obliquely relative to the paper conveying direction so that the driven roller can supply a conveying force for conveying the paper in the paper conveying direction and the direction perpendicular to the paper conveying direction (i.e., the alignment direction). The conveying force in the direction perpendicular to the paper conveying direction can align the sides of the paper to the aligner 3, so that the skew correction for the paper can be achieved.
The aligner 3 is fixedly mounted on the guiding part 1 in the double-sided printing paper conveying unit described above, thus alignment for paper based on the size of the paper cannot be performed as required during the double-sided printing. That is, when the paper conveying unit is used by a user to convey and align paper based on the size of the paper, there is a high probability that paper jam occurs in the imaging apparatus due to a mismatch between the size of the paper and the position of the aligner, or there is a difference between the typesetting of the image on the printed paper from a desired typesetting. Therefore, it is desired to provide a double-sided printing paper conveying unit capable of conveying and aligning paper based on the size of the paper.